Heat-treating silicon steel



July l5, 1952 N. B. oRNlTz 2,603,578

HEAT-TREATING SILICON STEEL Filed March 11, 1950 Figi. 22

INVENTOR steel.

,portingV the hot silicon steel.

V.silicon `carbide inserts.

Patented July 15, 1952 UNITED STATES PATENT! "o1-Fica HEAT-TREATING sILICoN's'TEEL Nathaniel B. 0mm, Pittsburgh-gra., assigner to Blaw-Knox Company, Pittsburgh, Pa., a corporation of New Jersey v Application March 11, 1950, Serial No. 149,079 l 6 Claims. (Cl. 148-16) n v Y 1 This invention relates to heat treating silicon It has to do specifically with the heat treatment of silicon steel at high temperature.

.The .invention provides an improvement in the rcopending `application Serial No, 74,451, filed .February 3, 1949, now abandoned.

` Silicon steel in sheet form (sheets or strip) is heat treated at high temperature (1600"y F. and

above) not only to remove rolling strains but also .to enhance the electrical properties of the steel.

As is known to those skilled in the art, such treatment poses a serious problem inA sup- The conveyor elements Aand the steel are at high temperature and it has been found that conveyor elements such as supporting rolls of usual composition tend to collect accretions of material from the steel which dent the steel passing over or around the conveyor elements. In the heat treatment of silicon steel at high temperature the higher the silicon content of the steel the more acute is theproblem. However, the phenomenon of .accretion formation is complex and is also influenced by the tension of the strip passing `around the rolls when the steel is in strip form,

nealing sheets, it has been found that in con- `tinuousstrip heat treating furnaces in which silicon vsteel strip is being heat treated at high temperature where the 'strip Wraps around the rollsunder tension some accretions form even on Furthermore, the provision and application of the refractory inserts entails substantial labor and expense.

In copending applications Serial No. 65,384., led December l5, 1948, and Serial No. 71,886, filed January 2l, 1949, are disclosed furnace conveyor elements comprising metal bodies having oxide coatings on the Work-carrying portions thereof, which oxide coatings inhibit the formation of accretions on the conveyor elements. While the conveyor elements of ,those applications have proved satisfactory, especially in high oxidizing atmospheres or in the lower ranges of strip tension, I have devised' an improvement ,each e of which has advantages. 40.

.resistant to oxidation.y

f Which ,which has broader application. By improvesertsor oxide coatedfconveyor elements. Inl the practice of my improvement I desirably employ anr improved conveyor element which has materially increased strength for -the quantity of costly high temperature alloy used in-.its manufacf I have discovered thatif the work-contacting portions of the conveyor elements are carbonaceous they provide a .suitable support, .have a satisfactory life and do.' not pick up 'accretions I' find that the heat treatment athigh temperature of silicon steel Which is supported by carbon during the heat treatment can be effectively and efciently carried out while the carbon supporting the-,steel has long Vlifewand is structurally strong. i y.

For example, when silicon steel is to be' decarburized it is vpreferably in sheet vformand is desirably strip steel. It is preferablyv continuously moved through a chamber under decarburizing conditions, the chamber desirably containingv a hydrogenous atmosphere, and is at a temperature above 1600 F. Vduring atleast a portion of its movement through the chamber. I supportthe ystrip by carbon during its movement through the chamber.v I desirably continuously' draw the silicon steelstrip about rotatable rolls through the ldecarburizing chamber-and provide'the rolls with jcarbonaceous lwork supporting `portions vwhich engage and-support lthe silicon Asteel-.strip during its movement through the chamber. The rolls maybe carbon-faced rolls cooperating with the strip so that only carbon touches the strip in .the decarburizingl chamber.` The rolls may be faced with either graphite or amorphous carbon, Graphite is stronger than amorphous carbon incompression and shear, .is moreeasilymachined and vis-more y Amorphous carbon is moreresistant to wearand lower in cost. g

Other details, objects and advantages ofthe invention will become apparent as the following .description of a present preferred method of practicing the same proceeds.

In A.the ,accompanying drawings- I `have illustrated a vpresent preferred method of practicing the. invention and have shown present preferred apparatus for use in practicing the invention in Figure 1 is a diagrammatic view of a decarburizing chambershowing how strip is supported for passage therethrough; y 1

Figure 2 is a view partly in elevation and partly Y in axial cross section of one of the rolls employed for supporting the strip in the decarburizing chamber; and

Figure 3 is an end view of the roll shown in Figure 2.

JrReferring now more particularly to the drawings, and rst to Figure 1, there is shownV a furnace chamber designated generally by reference f numeral 2Uvthrough which siliconV steel strip 2| is adapted to be drawn, the strip passing over a series of rolls at the top of the furnace and belneath a series of rolls at the bottom of thefur- The exact composition of the atmosphere is not 1.

of moment; in a hvdrogenousy atmosphere the chief ,active agent is hydrogen. The hydrogen is normally diluted with nitrogen and the atmosphere may also contain other ingredients such as water vapor and carbon monoxide. The hydrof gen of the atmospherevcombines with carbon of the silicon steel forming methane. Instead of a A.hydrogenous atmosphere other suitable atmospheres may be used; for example, an atmosphere 'containing a significant quantity of carbon monoxide. The decarburizing process per seV is known. n Y

As indicatedV above I have discovered thatY if the rolls 22 are provided with carbonaceous worksupporting portions which engage and support `the' silicon steel strip during its movement through the chamber accretions will not form on the'rolls and the disadvantages of accretion formation as referred to above are thus avoided. 'I'he rolls 22 may assume various forms, one form being shown in Figures 2 and 3. lReferring to ithose gures, each of vthe rolls 22 may comprise r a metal body designated generally by reference numeral 2 and a carbon sleeve 3. The sleeve 3 may, as above indicated, be of either graphite or amorphous carbon. The roll body 2- comprises "a barrel 4, two shaft ends 5, two drive rings 6y Aand vtwo closure plates 1, the shaft ends Bbeing lled 'with heat insulating material 8. The barrel 4, the shaft end s 5, the drive rings 6 and the vthe sleeve 3 anda vent I 0 establishing communication between the outside and the inside of the barrel 4 to permit venting of heated air from withinthe barrel when the roll'is brought up to temperature and entranceintothebarrel of air 4from the outside when the barrel cools 4and the heated air within contracts. The shaft ends 5 fhave cylindrical .portions II tting within the v'endsof the'barrel 4, taperedportions .I2 and cylindrical end .portions I3 and I4 of relatively great and relatively small diameter. The roll may be mounted for rotation in conventional :The ends of the'barrelkare -welded .to the shaft en ds 5-by weldsIS.V "The `closureplates' 4 are welded to the shaft ends 5 by welds I6. The drive rings 6 are welded to the barrel 4 by welds I1, but one of the drive rings is not applied and welded to the barrel until after the sleeve3 has been put in place on the barrel. Each of the drive rings 6 has a series of circumferentially spaced radially and axially extending projections I8 each of which entersla slot I9 provided therefor in one of the ends of the sleeve 3 thus Vlocking the sleeve to the roll body so that the roll functions as a unit.

The sleeve 3 constitutes the work-engaging portion of the roll and its outer cylindrical surface is the work-engaging surface of the roll. If the sleeve is made of graphite finely divided particles of graphite may be bonded with a sultablebinder, such, for example, as bituminous material such as tar, compressed into hollow cylindrical shape as shown and baked. The slots I9 may be molded into the sleeve at the time of its formation or may be cut out afterward. VA sleeve of amorphous carbon may be made'by baking in akiln a mixture of Yanthracite coal, petroleum coke and pitch. An amorphous carbon sleeve may be changed into graphite 'by being further heated in a graphitizing furnace to effectV transition of the carbon to graphitic form.

When the parts are cold the outside diameter of the circumferential projections 9 is slightly less than the inside diameter of the sleeve s0 that the sleeve may easily be applied over the barrel. However, when the roll is brought up to temperature expansion of the barrel resultsin a tight iit between the barrel and the Vsleeve so that the sleeve tightly embraces the roll body.

rThe carbonaceous work-engaging surface of the roll is superior to silicon carbide and also superior to the oxide surfaces disclosed in the abovementioned applications in inhibiting accretionA formation. Moreover, even with high strip tension the strip-engaging surfaces of the rolls 22 are maintained smooth by use, perhaps even somewhat improved and polished, which is just the reverse of the behavior of other rolls.

While I have shown and described a present preferred method of practicing the invention it is to be distinctly understood that the invention is not limited thereto but maybe `otherwise variously practiced within the scope of the following claims.

I claim:

1. In the lheat treatment of silicon steel in which silicon 'steel is heated to a temperature above i)o F., supporting the silicon steel by 4carbon during the heat treatment to inhibit formation of accretions on the supporting means.

2. In the Vdecarburizing of silicon sheet steelv in which silicon sheet steel is moved through 'a chamber containing a hydrogenous atmosphere and is at a temperature above 1600" F. duringjat least a portion'of said movement, supporting the silicon sheet steel by carbon during such '.move'- ment to inhibit formation of accretions on vthe supporting means. t

3. In the heat treatment of silicon steel strip in which silicon steel strip is continuously moved through a chamber containing a non-oxidizingA atmosphere and is at a temperature above 1600" F. during at least a portion of said movement, supporting the siliconsteel strip by carbon during such movement torinhibit formation of accretions on the supporting'means I 4. vIn the heat treatment of silicon steelstrip in which silicon steelstrip is continuously moved through a chamber containing an atmosphere 5 at a temperature above 1600 F. during at least a portion of said movement, drawing the silicon steel strip through the chamber about carbonfaced rolls so that only carbon touches the silicon steel strip in the chamber to inhibit formation of accretions on the rolls.

5. In the heat treatment of silicon steel in which silicon steel is heated to a temperature above 1600 F., supporting the silicon steel by graphite during the heat trearnent to inhibit formation of accretions on the supporting means.

6. In the heat treatment of silicon steel in which silicon steel is heated to a. temperature above 1600 F., supporting the silicon steel by amorphous carbon during the heat treatment to inhibit formation-of accretions on thesupporting means.

NATHANIEL B. onirrz.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS 

1. IN THE HEAT TREATMENT OF SILICON STEEL IN WHICH SILICON STEEL IS HEATED TO A TEMPERATURE ABOVE 1600* F., SUPPORTING THE SILICON STEEL BY CARBON DURING THE HEAT TREATMENT TO INHIBIT FORMATION OF ACCRETIONS ON THE SUPPORTING MEANS. 